Thorium and MSR Fuel Strategies

Kirk Sorensen, Flibe Energy

Oak Ridge National Laboratory October 5, 2016 The production of long-lived nuclear waste has been a potent focus of opposition to nuclear power for many years. Because of the failure of the US government to take custody of spent nuclear fuel, it remains at the same site at which it was produced. This was once the site of the Connecticut Yankee reactor. Even after a nuclear power plant site has been decommissioned, the "orphaned" spent nuclear fuel remains on site in casks. These spent fuel casks cannot legally be moved from the decommissioned reactor site and prevent its release for unlimited use. They also require continuous security. For millions of people each year, receiving a diagnosis of cancer is a terrifying moment that leads to profound uncertainty. Targeted therapies look very promising against cancer, especially against dispersed cancers like leukemia and lymphoma. They seek out cancer cells, destroying them with chemicals or radiation while leaving healthy cells alone. Targeted Alpha Therapy using Bismuth-213

Bismuth-213 has a 45-minute half-life (perfect) and decays from actinium-225, which has a 10-day half-life (perfect). It is near the end of its decay chain, and can be suitably chelated (wrapped in a chemical cage) and attached to an antibody that will hunt down and attach to a bloodborne cancer cell. When it decays, the alpha particle it emits will kill the cancer cell.

This is called targeted alpha therapy (TAT). TAT is a Smart Bomb Against Cancer

Precision Explosive Specific Target Guidance & Payload Target Destruction Delivery System

213 Bi monoclonal antibody cancer cell programmed cell death (apoptosis) 1.500kb

233Th 1.0%

7.282b 22.3m

15.00b β− α 232 24.8mb Th

14.1 Gyr 38.29b 100.00% 233Pa 7.2mb 27.0d

β−

51.31b

α 233U 91.2% 8.6mb 159.2 kyr

530b

Glenn Seaborg first created uranium-233 from thorium in April 1941 and correctly predicted that it was the first of a new family of radioactive materials. Candidate Alpha Emitters on the Decay Chains

Uranium 232 233 238 234 235

Protactinium 234 231

Thorium 232 228 229 234 230 231 227

Actinium 228 225 Actinium-225 227

Radium 228 224 225 226 223

Francium 221 223

Radon 220 222 219

Astatine 217 Astatine-211 211

Polonium Bismuth-212216 212 213 218 214 210 215 211

Bismuth 212 213 Bismuth-213209 214 210 211 207

Lead 212 208 209 214 210 206 211 207

Thallium 208 209 207

Thorium (+0) Neptunium (+1) Uranium (+2) Actinium (+3) Bismuth-213 is formed from the decay of Uranium-233

A million grams of uranium-233 will produce about 4 grams of thorium-229 each year. This thorium-229 will then produce alpha-emitting medicines (actinium-225 and bismuth-213) for thousands of years. Possible Nuclear Fuels

Natural Thorium Natural Uranium 100% thorium-232 99.3% uranium-238 0.7% uranium-235

Only a small fraction of natural uranium is fissile. Most uranium and all thorium is "fertile" and can be converted to fissile material through neutron absorption. Nuclear Conversion Reactions

Fission Product

time for Uranium 9,000 MWh(e)/kg Thorium decay 233 2.3 (net) neutrons

Fission Product neutron neutron Thorium and uranium-238 both require two neutrons to release their energy: one to convert them to fissile fuel and another to release their energy through fission. But only thorium produces sufficient neutrons (2.3) in thermal reactors to sustain energy release.

Fission Product

Uranium time for Plutonium 9,000 MWh(e)/kg 238 decay 239 1.9 (net) neutrons

Fission Product

neutron neutron Energy from thorium

1.500kb I Abundant, natural thorium is the starting point in the process 233Th 1.0% I Thorium absorbs a neutron, 7.282b 22.3m forming short-lived thorium-233.

15.00b β− I Thorium-233 quickly decays in α 232 24.8mb Th protactinium-233, which is

14.1 Gyr 38.29b 100.00% chemically distinct from thorium. After a little more than a month, 233Pa I 7.2mb protactinium-233 will decay into 27.0d uranium-233, which is the best β− nuclear fuel.

51.31b I The fission of uranium-233 releases energy and sufficient α 233U 91.2% neutrons to continue the process. 8.6mb 159.2 kyr

530b Nuclear Conversion Reactions

Fission Product

Uranium time for Plutonium 9,000 MWh(e)/kg 238 decay 239 2.3+ (net) neutrons

Fission Product

neutron fast neutron Using fast neutrons improves the performance of the uranium fuel cycle sufficiently to allow sustained further conversion and fission reactions. This has been the basis of global interest in fast-spectrum reactors for nearly 70 years. Thermal vs. fast neutron cross-sections

Uranium can be a sustainable fuel in a fast reactor, but using fast neutrons comes at a substantial price. Neutron cross-sections are much smaller for fast neutrons than for thermal (slowed-down) neutrons. To a thermal neutron, one atom of plutonium-239 is the equivalent of nearly 700 atoms of plutonium-239 to a fast neutron. This is why thermal reactors have a far lower fuel inventory than fast reactors, and why almost every reactor in the world today is a thermal reactor. Starting with Uranium is Inevitable tr nmt decay ansmute fission

Uranium Uranium Plutonium

235 neutrons 238 239

Starting with uranium is inevitable since uranium-235 is the only natural fissile material. A well-designed reactor will essentially "burn out" its uranium-235 inventory while producing chemically-separable plutonium. Depending on the exposure duration small amounts of other transuranics will also form. Today’s nuclear fuel is fabricated with extraordinary precision, like a fine watch.

But it is that precision that makes it difficult to recycle and to refabricate. A new approach is needed that is more versatile and less expensive. Spent Nuclear Fuel Composition 0%

Very-low radioactivity, unused uranium fuel 1%

2%

Highly radioactive, but 3% rapidly decaying fission products with a variety of potential applications

4%

Low-lived, fairly radioactive 5% “transuranic” isotopes, with potential for consumption in a reactor; drives disposal concerns

6% Very-low radioactivity, unused uranium

Fresh fuel 1 year 2 years 3 years The Traditional Plan for Nuclear Utilization

recycle

Plutonium Uranium neutrons Plutonium 239 238 239 fission ansmute decay Phasetr 2: Plutonium breeding tr nmt decay ansmute fission

Uranium Uranium Plutonium

235 neutrons 238 239

Phase 1: Uranium-235 consumption Sustainable Use of Thorium is the Ultimate Goal

recycle tr nmt decay ansmute fission

Uranium Thorium Uranium

233 neutrons 232 233

Uranium-233 alone produces sufficient neutrons per thermal neutron to match or exceed its consumption. In this way, U-233 is the "catalyst" to sustainable energy production from thorium and can almost eliminate transuranic production. But very little U-233 presently exists, and not enough for a major rollout of thorium reactors. Reactor Containment Boundary Decay Salt (HDLiF-BeF2-ThF4-PaF4) Bismuth 32 Blanket Salt (HDLiF-BeF2-ThF4) F2 40 Fuel Salt (HDLiF-BeF2-UF4) UF6-F2 34 33 35 Coolant salt (HDLiF-BeF2) HF-H2 Rede Rede

Electro Higher-pressure CO2 (200 bar) H2 41 Lower-pressure CO2 (77 bar) 2 x 1 x Cooling Water

35 31 2 33 Generator 1 270 MW 39 6 8 Wet 38 Gas ThF4 Cooling 36 52

UF6 Heater makeup Turbine 51 600 MW

HF 5 384 MW Reduction 7 19 9 Decay Electro Primary Tank 20 HX 14 600 MW 50 Gas Cooler 37 Compressor 3 322 MW 48 Lo-temp 39 MW 13 21 Hi-Temp 4 recuperator 43 49 47 986 MW 44 12

Fluor Fluor Compressor 18

Rede Freeze valve Drain Med-temp ntr1 inator ntr2 inator 75 MW Tank 17 3 x

45 10 11 Lo-Temp 42 46 recuperator 53 54 399 MW 16 15 Liquid-Fluoride Thorium Reactors (LFTR) are reactors that use uranium-233 as their fuel, generated from abundant natural thorium. By using uranium-233, they also form the medicinal precursors needed for targeted alpha therapy. Under the leadership of Alvin Weinberg, Oak Ridge National Laboratory led the effort to develop thorium as an energy source. Uranium-233 generated from thorium was first used to power a reactor in 1968, and ORNL has been the home to the US supply of uranium-233 every since. Uranium-233 Inventories in DOE

There are valuable materials at INL and ORNL that could greatly accelerate thorium reactor development. In particular, the inventory of 233 ThO2/ UO2 fuel developed for the 1978 “Light Water Breeder Reactor” contains: I 351 kg of 233U I 14,000 kg of thorium This fuel could be fluorinated into ThF4 and UF4 and combined with LiF-BeF2 salts to form the fuel and blanket salts of a reactor that would thereafter produce ~300 MWe of sustainable power generation. Consume Plutonium or Generate More Plutonium?

recycle tr nmt decay ansmute Plutonium is the fission inevitable result of the first stage of Plutonium Uranium Plutonium nuclear utilization.

239 neutrons 238 239 WIth uranium, it cannot make more fissile than it consumes (in tr

nmt decay ansmute thermal reactors). fission But with thorium, Plutonium Thorium Uranium plutonium fission

239 neutrons 232 233 generates the U-233 that is the key to sustainability. Use Thorium for Transition from Plutonium tr nmt decay ansmute fission

Plutonium Thorium Uranium

239 neutrons 232 233

So consuming plutonium as fuel in a reactor with thorium can produce the uranium-233 needed to "bridge" to sustainable thorium-fueled reactors. Three-Phase Plan to Sustainability

Uranium Uranium Uranium 235 233 233

fission neutrons transmute decay fission neutrons recycle Uranium Thorium Thorium 238 232 232

transmute decay fission neutrons transmute decay

Plutonium Plutonium Uranium 239 239 233

Phase 1 Phase 2 Phase 3 U-235 consumption U-233 production Thorium consumption Better Fuel Strategies for MSRs

recycle tr nmt decay ansmute A chloride MSR (fast fission spectrum) could breed more fuel than Plutonium Uranium Plutonium it consumes, using

239 neutrons 238 239 the U-Pu cycle. This has been proposed for fast chloride MSRs. tr nmt decay ansmute fission

Fission of U-235 Uranium Thorium Uranium (essentially HEU)

235 neutrons 232 233 could permanently consume it while the neutrons form U-233 from thorium. This approach could skip to Phase 3. Best Fuel Strategies for MSRs

recycle tr nmt decay ansmute U-233 fuel fission irradiating Th-232 can breed in the Uranium Thorium Uranium thermal spectrum

233 neutrons 232 233 and almost eliminate transuranic production. This is Phase 3. tr nmt decay ansmute fission Consuming TRU in the presence of Plutonium Thorium Uranium Th-232 forms U-233

239 neutrons 232 233 while permanently destroying TRU. This is Phase 2. LFLEUR chemical processing Scr ub

KOH Decay Tank

H2 Bi(Pa,U) Bi(Th)

Reduction metallic Th feed W seFluorinator aste decontaminated uranium tetrafluoride for conversion to U3O8 and disposal purified UF6 Bi(TRU) Bi(Li)

chopped and decladded Rotary inated TRU + FP spent nuclear fuel Voloxidizer fluor barren fuel salt + FP

fuel powder barren Hydrofluor Freeze valve Drain are salt carrier Tank aste salt inator w inated spent nuclear fuel w

sesl FP + salt aste metallic

fluor Bi(FP) Bi(Li) HF HDLi feed Voloxidation

3UO2 + 2NO2 → U3O8 + 2NO

2NO + O2 → 2NO2

Spent nuclear fuel is first oxidized with nitrogen dioxide which causes it to pulverize into a fine powder. Xenon, krypton, tritium, iodine, and CO2 are removed as gases and purified and separated. Hydrofluorination

(U,Zr)O2 + 4HF → (U,Zr)F4 + 2H2O

(Rb,Cs)2O + 2HF → 2(Rb,Cs)F + H2O

(Sr,Ba)O + 2HF → (Sr,Ba)F2 + H2O Ln2O3 + 6HF → 2LnF3 + 3H2O

MoO3 + 6HF → MoF6 + 3H2O

Next the powdered fuel is reduced with hydrogen and hydro-fluorinated to replace all oxides with fluorides. The constituent materials change from oxides (ceramics) to fluorides (salts) as oxygen in the spent fuel is removed as water vapor. Fluorination Uranium is removed from the salt mixture through fluorination to gaseous uranium hexafluoride. Several other constituents also form gaseous hexafluorides, but most do not. Fluorination is one of the most challenging chemical processes because of its severity on any container material.

UF4 + F2 → UF6

NpF4 + F2 → NpF6 Fluorination using NF3 Alternatively, nitrogen trifluoride (NF3) might be used for fluorination instead of gaseous fluorine (F2). NF3 is much less aggressive towards container materials.

2UO3 + 4NF3 → 2UF6 + 2N2 + 3O2

3NpO2 + 4NF3 → 3NpF4 + 2N2 + 3O2 2Ln2O3 + 4NF3 → 4LnF3 + 2N2 + 3O2

2MoO3 + 4NF3 → 2MoF6 + 2N2 + 3O2 LFLEUR chemical processing Scr ub

KOH Decay Tank

H2 Bi(Pa,U) Bi(Th)

Reduction metallic Th feed W seFluorinator aste decontaminated uranium tetrafluoride for conversion to U3O8 and disposal purified UF6 Bi(TRU) Bi(Li)

chopped and decladded Rotary inated TRU + FP spent nuclear fuel Voloxidizer fluor barren fuel salt + FP

fuel powder barren Hydrofluor Freeze valve Drain are salt carrier Tank aste salt inator w inated spent nuclear fuel w

sesl FP + salt aste metallic

fluor Bi(FP) Bi(Li) HF HDLi feed Flibe Energy was formed in order to develop liquid-fluoride reactor technology and to supply the world with affordable and sustainable energy, water and fuel. Through liquid-fluoride reactor technology, thorium will become the world’s dominant energy source, and this will be the key economic driver of the twenty-first century.

And likely beyond.